decide指经过思考、询问和讨论后做出判断或决定去做某事。如：
Professor Wang's words decided her to catch up with others. 王教授的话使她下决心赶上其他人。
I decided to take the position at the bank. 我决定接受在银行的职位。
make up one's mind是hesitate(迟疑), be puzzled(迷惑不解)等词的相对说法，表示不再犹豫不决。如：
Have you made up your mind how to do it? 你已经拿定主意怎样做这件事了吗？
She made up her mind that she would win. 她决心争取胜利。